Control apparatus using thermoelectric power



June 30; 1959 R. B. MATTHEWS 2,

CONTROL APPARATUS USING THERMOELECTRIC POWER Filed Nov. 25, 1955IIIIIIIIIIIIIIIIIII IN VEN TOR: RUSSELL B. MATTHEWS BY Ai *ZW ATTORNEYSUnited States Patent CONTROL APPARATUS USING THERMO- ELECTRIC POWERRussell B. Matthews, Wauwatosa, Wis., assignor, by

mesne assignments, to Minnesota Minin and Manufacturing Company, St.Paul, Minn., a corporation of Delaware Application November 25, 1955,Serial No. 549,074

11 Claims. (Cl. 236-9) This invention relates to improvements in controlapparatus and more particularly to control apparatus powered from a lowpower direct current source, for example a thermoelectric generator.

One of the limitations of control circuits powered from low voltagesources, for example thermoelectric generators, is that transmissionlosses are relatively high and therefore the length of the circuit leadsor conductors must be kept relatively short in order to be able toutilize this low voltage power in the performance of use- [ful work.

With this in mind it is a general object of the present invention toprovide in a control apparatus powered from a low power source, meansfor changing the voltage of the electric energy available from saidsource to a higher voltage for the energization of a control circuit,the said higher voltage permitting extension of the leads of saidcircuit to a location remote from said source, for example to a remotelylocated thermostat.

More specifically, it is an object of the invention to provide animproved control apparatus of the aforementioned character having novelmeans for converting the output of a low voltage direct current source,for example, a thermoelectric generator to a pulsing direct current andfor feeding said pulsing current into the primary winding of a step-uptransformer for induction into the secondary Winding of said transformerof a higher voltage alternating current operable to energize the controlcircuit. 7

Another specific object of the invention is to provide an improvedcontrol apparatus of the class' described wherein the pulsing directcurrent is produced by a continuously cycling device for successivelyinterrupting and remaking the low voltage direct current circuit, saiddevice including temperature responsive contact actuating means andheating means energized by the current flow in said direct currentcircuit when the contacts are in circuit-making position, said contactactuating means being responsive to the heat produced by said heatingmeans for moving the contacts to circuit-interrupting position andterminating said heating action for reengagement of the contacts and thebeginning of a new cycle.

Another object of the invention is to provide means operatively'relatedto the temperature responsive contact actuating means for rendering theoperation of the circuit interrupting and remaking device independent ofchanges in the ambient temperature.

Other and further objects of the invention will become apparent as thedescription proceeds, reference being had to the accompanying drawingillustrating one form of the invention, wherein:

Figure 1 is a semi-diagrammatic view of a fluid fuel burning apparatusequipped with control apparatus constructed in accordance with theinvention; and

Figure 2 is an enlarged longitudinal sectional view showing theconstruction of the preferred thermoelectric generator for powering thecontrol apparatus shown in Figure 1. l

Referring now to Figure l of the drawing, the numeral 10 indicates amainfuel burner which is supplied with fluid fuel under pressure througha supply conduit 11 which has a cycling type electromagnetic valve 12interposed therein. The electromagnetic operator of the valve 12comprises an electromagnet 13 having an energizing winding 13a having arelatively large number of turns as compared with the number of turnsusually found in the electromagnets of thermoelectrically poweredcycling type valves. An armature 14 cooperates with pole faces of theelectromagnet 13 and is can ied by a reversely bent pivotal arm 16 whichalso carries a valve member 15 as shown. The arm 16 preferably includesa resilient energy storing portion, and a spring 17, acting through thearm 16, biases the valve members 15 toward its seat 18 and the armature14 towardretracted position with respect to the pole faces of theelectromagnet 13.

A pilot burner 20 is disposed in igniting relation with respect to themain burner 10 and may be supplied with fuel through a conduit 19. Athermoelectric generator, which preferably takes the form of athermocouple 31 having at least one semi-metallic element, is mountedadjacent the pilot burner 20, \for example by a bracket 32, with its hotjunction subject to the heat of burning fuelat the pilot burner 20. Oneof the terminals of the generator 31, for example the lead conductor 55,is connected to one end of the primary winding of a step-up transformer40, as by a conductor 34, and the other teminal of said generator, forexample the lead conductor 54 is connected to the other end of saidprimary transformer winding, as by a conductor 33. One end of thesecondary winding 42 of the transformer 4i) may be connected to oneinput terminal of a full wave rectifier as by a conductor 36, and theother end of said secondary winding may be connected to the otherinputterminal of the rectifier 70, as by conductors 37 and 38 which mayextend to a remote location for connectionof 'a thermostat 39 in seriescircuit relation with respect to the winding 42 and rectifier 70. Theoutput terminals of the rectifier 70 may be connected in circuit withthe winding 13a by conductors 71 and 72 as shown.

Means in the form of a continuously cycling device 23 is interposed inthe conductor 33 as shown for successively interrupting and remaking theelectrical circuit between the generator 31 and the primary winding 41at predetermined intervals to thereby supply said primary winding with apulsing direct current. The device 23 comprises a metallic expansibleand contractible hermetically sealed enclosure which may take the, formof a cylindrical bellows of relatively thin gauge brass or othersuitable electrically conductive material. The bellows 24 has opposingend walls 25 and 26, and sealingly and insulatably extending through theend wall 25 is a contact 27 which is cooperable with a relativelymovable contact 23 carried by and in circuit with the end wall 26. Themounting for the contact 27 preferably also provides for the mounting ofa connecting lug 29 in circuit with the end wall 25 as shown. The lug 29and the contact 27 are connected in circuit with contiguous sections ofthe conductor 33 as shown. The contacts 27 and 28 are preferably made oflow resistance metal, for example silver, and disposed within thebellows 24 is a temperature responsive expansible and contractible fillwhich does not deleteriously affect the low resistance character of thecontacts. Preferably the fill takes the form of a volatile fluid whichis substantially non-conductive electrically, one example of which ispentane.

For a purpose which will hereinafter appear, a bellows 43, which may beidentical with the bellows 24 and may contain the same fill, is providedwith an end wall 68 which may fixedly abut a suitable fixed support 70,

Patented June 30, 1959.

stress on the bellows 24 and 43 to bias the contacts 27 and 28 towardcircuit-making position, and said means may take the form of acompression spring 45 acting through an abutment member 44 engaging thebellows end wall 25. The bias of the spring 45 may be adjusted by meansincluding a rotary cam 47 engaging a thrust plate 46 which coacts withend of the spring 45 opposite the abutment member 44 as shown.

Referring now to Figure 2 of the drawing, the thermoelectric generator31 illustrated therein comprises a pair of thermocouple element means 48and 49, the latter of which takes the form of an elongated generallycupshaped sheath member, preferably of stainless steel. The sheath 49has a tubular sleeve portion 50 and a tip portion 51 which may serve asa heat probe means for the assembly. The opposite end of the member 49is telescopically received within a counterbore formed within one end ofan extension tube 52 of brass or other suitable material and issealingly fixed therein, as by silver soldering or brazing at 67. Theother end of the extension tube 52 is formed with a portion of reduceddiameter to snugly receive one end of a coaxial type thermoelectricgenerator lead 53, comprising a metallic tubular outer conductor 54 andan insulated coaxial inner conductor 55. The sleeve 52 has an end recessadjacent the lead 53, and said tube and lead are sealingly andelectrically connected, for example by silver soldering or brazing, at56.

The thermocouple element means 48 preferably comprises a rod-like orcylindrical ingot of semi-metallic alloy or composition disposed incoaxial spaced relation within the sheath 49. Because the thermocoupleelement means 48 is of frangible material, the generator is constructedin a manner to provide shock resistant mounting means therefor. Theelement means 48 includes an iron contact electrode 57 having a stemportion 58 formed with a shoulder 59. The tube 52 is formed with aninternal annular shoulder 60, and surrounding the contact electrode stemportion 58 is an insulating washer 61 engaging the shoulder 60.interposed between the insulating washer 61 and the stem shoulder 59 isa compression spring 62 which may take the form of a concavo-convexcentrally apertured resilient disc also surrounding the electrode stem58.

The sheath 49 is formed with a conical inner end wall surface 63, andthe semi-metallic element 48 is formed with a complementary conical endwall surface 64 which is seated against the end wall surface 63. Thespring 62 exerts compressive stresses on the element 48, which stressessubstantially reduce the net tensile stresses to which said element issubjected during transverse acceleration or shock, said compressivestresses not being so high as to exceed the compressive strength of saidelement. The bias of the spring 62 also provides the pressure necessaryfor a satisfactory pressure contact between the element 48 and thesheath 49 at the surfaces 63 and 64. The pressure type contact is notdeleteriously effected by deformation of the element 48, for example onbending under transverse shock, and the conical nature of the surfaces63 and 64 tends to maintain the biased element 48 in centeredrelationship within the tubular portion 50 of the member 49. Thecompressive stress under which the member 48 is placed increases themagnitude of deformation which said element can withstand withoutfracture and affords the generator 35 substantial shock resistance.

A tube 65 of insulating material preferably surrounds the contactelectrode stem 58, and a flexible conductor 66'. extends within the tube65 and affords an electrical connection between the stem 58 and theinner conductor of the coaxial lead 63.

The thermocouple element 48 may, for example, be formed of asemi-metallic alloy or composition which may be characterized as abinary metallic compound of slightly imperfect composition, i.e.containing beneficial impurities constituting departures from perfectstoichiometry by reason of an excess of one of the metals over theother, and/or containing added beneficial impurity substanceshereinafter referred to as promoters. Such semi-metallic compositionshave semi-conductor like conductance, both electrical and thermal, andinclude mixtures of such binary metallic compounds, which may bedenominated ternary metallic alloys or compositions. Certain of thesealloys or compositions exhibit negative and certain exhibit positiveelectrical characteristics.

More specifically, the thermocouple element 48 may, for example, beformed of an alloy further described in the copending application ofSebastian Karrer, Serial No. 475,540, filed December 15, 1954, nowPatent No. 2,811,570, and assigned to the assignee of the presentinvention, said alloy comprising lead and at least one member of thegroup tellurium, selenium and sulphur. For example, a thermoelectricelement 48 of lead-seleniumtelluriurn composition could include atellurium-selenium constituent in which the selenium is but a trace. Inthis case such constituent should constitute from 35% to 38.05% byweight of the composition, the balance (61.95% to by weight) being lead.At the other extreme, where the tellurium-selenium constituent con sistsalmost entirely of selenium with but a trace of tellurium, suchconstituent should comprise from 25% to 27.55% by weight of the finalcomposition, the remainder (from 72.45% to by weight) being lead.Between these two extremes, the selenium-tellurium constituent varieslinearly with the ratio of selenium to tellurium (expressed in atomicprecent) in the selenium-tellurium constituent.

The thermoelectric element 48 may also be formed of an alloy of lead,selenium and sulphur. For example, a thermoelectric element 48 of thelead-selenium-sulphur composition consist of a selenium-sulphurconstituent in which the sulphur is but a trace. In this case, suchconstituent should constitute from 25% to 27.55% by weight of thecomposition, the balance (75% to 72.45% by weight) being lead. At theother extreme, where the selenium-sulphur constituent consists almostentirely of sulphur with but a trace of selenium, such constituentshould comprise from 12.8% to 13.37% by weight of the final composition,the remainder (from 87.2% to 86.63% by weight) being lead. Between thesetwo extremes the selenium-sulphur constituent varies linearly with theratio of selenium to sulphur (expressed in atomic percent) in theselenium-sulphur constituent.

With regard to the aforementioned compositions, it will be observed thatin each case there is an excess of lead over and above the amountthereof necessary for satisfying the stoichiometric proportions of thecompound formed in the second constituent or constituents, i.e. thetellurium, selenium or sulphur. For example, the composition consistingsubstantially of lead and selenium can contain up to 10.4% lead byweight of the total composition over and above the 72.14% by weight leadstoichiometrically necessary for combination with seleniurn.

The electrical characteristics of the aforementioned semi-metallicalloys, desirable, for example in thermoelectric elements, can bemarkedly and advantageously altered in a reproducible manner by theaddition thereto of controlled amounts of matter other than theconstituents of the base composition. Such additions may also bedenominated beneficial impurities as distinguished from undesirableimpurities. For convenience. these additions are hereinafter designatedpromoters,

3 since they tend to enhance the electrical characteristics desired forthe particular application of the base composition.

The aforedescribed base compositions exhibit negative thermoelectricpower and negative conductivity. By the addition of certain promoters,such negative properties may be enhanced, While the polarity of theelectrical properties of the base composition may be reversed by theaddition of certain other promoters. The copending application of RobertW. Fritts and Sebastian Karrer, Serial No. 475,488, filed on December15, 1954, now Patent No. 2,811,571, and assigned to the assignee of thepresent application, gives a complete description of the beneficialimpurities, including both departures from perfect stoichiometry andpromoters, which have been found to be efiective for improvement of theelectrical properties of semi-metallic thermoelectric generator elementswhen added to the aforementioned base compositions in minor amounts, forexample up to a maximum of 6.9% by weight of beneficial impurity,including 3.9% excess lead and 3.0% promoter.

The proportions and ranges of the various constituents aforementionedand particularly the minimum limits of the lead constituent in thecompositions, must be regarded as critical if the composition is to havethe electrical and physical properties desired. If the lead content issignificantly less than the minimum amount indicated for any particularselenium-tellurium or seleniumsulphur proportion, the polarity of theSeebeck emf changes and the desired electrical and mechanical propertieswill not be reproducible. On the other hand, if the lead content of anycomposition appreciably exceeds the aforementioned maximum limits, theresulting composition is too metallic in nature to afford satisfactoryenergy conversion efliciencies.

Not only are the proportions and ranges aforedescribed to be consideredcritical, but so also is the purity. More specifically, the limit oftolerable metallic impurity in non-promoted final compositions has beenfound to be on the order of 0.01%, and the composition must besubstantially oxygen free, if the mechanical and electrical propertiesdesired are to be obtained and are to be reproducible. In the case ofpromoted compositions, however, the limit of tolerable impurity is0.001%.

In order to utilize any of the aforementioned base alloy or promotedcompositions in electrical devices, for example as thermoelectricgenerator elements, they must necessarily be electrically contacted. Aspreviously pointed out, electrical contact with the ingot 48 is made atone end with the inner wall surface 63 by means of a pressure contact.The electrical contact with the ingot at the opposite end, however, ismade by bonding of the contact electrode 57 with the end surface of theingot 48, and if desired, the aforementioned pressure contact can bereplaced by such a bonded contact. In the latter case theelement-electrode interface must have a mechanical strength at leastcomparable to that of the alloy of which the element 48 is made. Thecontact electrode must be chemically stable with respect to the element48 and provides the necessary means for connecting said element into itselectrical circuit while at the same time chemically isolating saidelement from the other conductors making up said circuit. Iron isespecially adapted for use as contact electrode material for elements 48of lead-tellurium-selenium composition, and pressure type contacts ofcarbon are suitable for elements 48 of any of the aforedescribedcompositions including those comprising lead and sulphur.

Since, as is well known in the art, the electrical and thermalresistance of the thermoelectric generator 35 are dependent upon theconfiguration thereof as well as on the electrical and thermalconductivities of the elements 48 and 49, the relationship between thedimensions of each element can be obtained which affords the highestthermal conversion efiiciency in such a mounting or assembly. In theembodiment described, the thermal con- 6 ductivity of the semi-metallicelement 48 is low as com pared with that of the element 49 (for example.025 watt/cm./ C. as compared to .261 watt/cm./ C.).

For elements of any given thermal and electrical conductivities, theconversion efliciency depends strongly upon the ratio of thickness ofthe sheath 49 to the radius of the element 48, or more specifically,upon the cross-sectional area of the tube. In the embodimentillustrated, this ratio of the radius of the element 48 to the thicknessof the sheath 49 is preferably about 6 to l or more.

It is understood, of course, that the conversion efiiciency of thethermocouple is also dependent upon the difference between the hot andcold junction temperatures. For thermocouples utilizing a semi-metallicinner element having a low thermal conductivity, high temperaturedifferences can be achieved by selecting for the semi-metallic element aratio of length to diameter, which in the exemplary embodiment hereindisclosed is about 4 to 1, such that radiation transfer of heat from thesurface of the inner element to the sheath establishes substantialtemperature gradients within the inner element, particularly near thehot junction. When this is done, the heat flux into the inner elementthrough the hot junction, i.e. the juncture of the faces 63 and 64 isexhausted to the case over the entire side wall surface of the innerelement, allowing the inner cold junction, i.e. the juncture of theelement 48 with the contact electrode 57, to assume a temperature onlyslightly greater than that of the outer cold junction, i.e. the junctureof the element 49 and sleeve 52. A further consequence of such radiativecooling is the reduced electrical resistance of the semimetallic element48, said element having a positive temperature coefficient ofresistance. The radiation responsible for the removal of the heattransmitted across the hot junction takes place between the element 48,its cold junction electrode 57, and the metal walls of the element 49and extension tube 52. Since the cold junction temperature under suchcircumstances is dependent upon the temperature of its environment, itis desirable to keep the ambient temperature low. The extension of thesheath to a cooler Zone, as by the extension tube 16, provides a heatsink which aids in cooling the casing around the cold junctions.

In the operation of the improved control apparatus, the thermoelectricgenerator 31 produces a relatively low voltage, for example less than avolt, direct current in response to heating of the tip portion 51thereof by the flame of the pilot burner 20, and this current flowsthrough the primary circuit afforded by the conductor 34, primarytransformer winding 41, conductor 33, contacts 2'7 and 28, end wall 26,the side wall of the bellows 24, end wall 25, lug 29 and conductor 33.By reason of the electrical resistance of the bellows walls, the flow ofthermoelectric current therethrough, which occurs when the contacts 27and 28 are in circuit-making position, produces a small amount of heatto which the fill within the bellows 24 is responsive to effectexpansion of said bellows and movement of the contacts 27 and 28 in aseparating direction to circuit-interrupting position. This, of course,interrupts the current flow through the primary winding 41 of thetransformer and also terminates the heating action produced by theaforementioned current flow through the bellows walls. The bellows 24and its fill thereupon, cool and the cooling of said fill effectscontraction of the bellows to return the contacts to circuit-makingposition for the beginning of another cycle.

The device 23 continuously cycles with preferably equal periods ofcurrent flow and current interruption. As a result of the successiveinterruption and remaking of the aforementioned primary circuit, apulsing low voltage direct current is supplied to the primary winding 41of the transformer 40. This low voltage pulsing direct current inducesin the secondary winding 42 of the transformer 40, an alternatingcurrent which, by virtue of the step-up character of the transformer, isof much higher voltage than that of said pulsing current for example 10to volts or higher if desired, said alternating current having, however,substantially the same frequency as the aforementioned pulsing directcurrent. The alternating current from said secondary winding is suppliedto the input terminals of the rectifier '70 which rectifies said currentfor delivery to the operator 13 as a direct current under the control ofthe thermostat 39. The thermostat 39 may be disposed in a space heatedby the heat produced by the main burner 10 for control of the flow offuel to the main burner in accordance with the requirements for whichthe thermostat is set. The relatively high voltage supplied by thesecondary winding 42 permits the thermostat 39 to be located remotelyfrom the transformer 40 if desired, since transmission losses at thehigher voltage are relatively low as compared with those at lowervoltages, for example those produced by the generator 31.

The response of the bellows 43 and its fill to changes in ambienttemperature, opposes the response of the bellows 24 and its fill to saidchanges, so that operation of the cycling device 23 is independent ofchanges in the ambient temperature, and a relatively constant cyclingfrequency is thereby maintained.

The improved cycling device 23 is characterized by its high sensitivityand low differential which permits quick response to the presence orabsence of thermoelectric current flow through the bellows walls. Thelow resistance character of the primary circuit including the walls ofthe bellows 24 and the contacts 27 and 28 provides for the mostefficient use of the current supplied by the generator 31, and as aresult, the device 23 cycles relatively rapidly, and the maximum amountof thermoelectric energy is supplied to the primary winding 41 forconversion to higher voltage alternating current by the transformer.

Having thus described one embodiment of the present invention, it is tobe understood that the illustrated form was selected to facilitate thedisclosure of the invention, rather than to limit the number of formswhich it may assume. Various modifications, adaptations and alterationsmay be applied to the specific forms shown to meet the requirements ofpractice without in any manner departing from the spirit or scope of thepresent invention, and all of such modifications, adaptations andalterations are contemplated as may come within the scope of theappended claims.

What is claimed as the invention is:

l. A continuously cycling device for successively interrupting andremaking an electric circuit at predetermined timed intervals,comprising relatively movable solid metal contacts normally biasedtoward circuit-making position, an hermetically sealed expansible andcontractible enclosure for said contacts having an electricallyconductive portion of predetermined electrical resistance, a temperatureresponsive expansible and contractible fluid fill for said enclosuresubstantially non-conductive electrically and responsive to apredetermined temperature for actuation of said contacts tocircuit-interrupting position, a source of electrical energy, and meansconnecting said enclosure portion and contacts in circuit with saidsource to effect current flow from said source through said contacts andenclosure portion when said contacts are in circuit-making position,current flow through said enclosure portion producing heat in responseto which expansion of said fill, after a predetermined time intervalfollowing making of said circuit at the contacts, moves said contacts tocircuit-interrupting position for interruption of said current flow andtermination of said heat generation to permit cooling of said enclosureportion and fill in response to which contraction of said fill, after apredetermined time interval following interruption of said circuit atthe contacts, returns said contacts to circuitmakiug position for thebeginning of another cycle.

2. A continuously cycling device for successively. interrupting andremaking an electric circuit at predetermined timed intervals,comprising relatively movable low resistance solid metal contactsnormally biased toward circuit-makiug position, and hermetically sealedexpansible and contractible enclosure for said contacts having anelectrically conductive portion of predetermined electrical resistance,a temperature responsive expansible and contractible fluid fill for saidenclosure substantially nonconductive electrically and responsive to apredetermined temperature for actuation of said contacts tocircuit-interrupting position, a thermoelectric generator having atleast one semi-metallic element, and means connecting said enclosureportion and contacts in circuit with said generator to effectthermoelectric current flow from said generator through said contactsand enclosure portion when said contacts are in circuit-making position,said current flow through said enclosure portion producing heat inresponse to which expansion of said fill, after a predetermined timeinterval following making of said circuit at the contacts, moves saidcontacts to circuitinterrupting position for interruption of saidcurrent flow and termination of said heat generation to permit coolingof said enclosure portion and fill in response to which contraction ofsaid fill, after a predetermined time interval following interruption ofsaid circuit at the contacts, returns said contacts to circuit-makingposition for the beginning of another cycle.

3. A continuously cycling device for successively interrupting andremaking an electric circuit at predetermined timed intervals,comprising relatively movable solid metal contacts normally biasedtoward circuitmaking position, an hermetically sealed expansible andcontractible enclosure for said contacts having an electricallyconductive portion of predetermined electrical resistance, a temperatureresponsive expansible and contractible fluid fill for said enclosuresubstantially nonconductive electrically and responsive to apredetermined temperature for actuation of said contacts tocircuitinterrupting position, a source of electrical energy, meansconnecting said enclosure portion and contacts in circuit with saidsource to effect current flow from said source through said contacts andenclosure portion when said contacts are in circuit-making position,current flow through said enclosure portion producing heat in responseto which expansion of said fill, after a predetermined time intervalfollowing making of said circuit at the contacts, moves said contacts tocircuit-interrupting position for interruption of said current flow andtermination of said heat generation to permit cooling of said enclosureportion and fill in response to which contraction of said fill, after apredetermined time interval following interruption of said circuit atthe contacts, returns said contacts to circuit-making position for thebeginning of another cycle, and ambient temperature responsive meansoperatively related to said enclosure for opposing expansion andcontraction thereof in response to changes in ambient temperature,thereby rendering the operation of said device independent of changes inambient temperature.

4. In combination, a thermoelectric generator having at least onesemi-metallic element, a step-up transformer having primary andsecondary windings, relatively movable low resistance solid metalcontacts having circuitmaking and circuit-interrupting positions,temperature responsive contact actuating means for continuously cyclingsaid contacts between said circuit-making and circuitintermptingpositions, said means comprising an expansible and contractiblehermetically sealed enclosure for said contacts having an electricallyconductive portion of predetermined electrical resistance, a thermallyexpansible and contractible fluid fill for said enclosure substantiallynon-conductive electrically, and means conmeeting said contacts andenclosure portion in circuit with said generator and the primary widingof said transformer to effect thermoelectirc current flow through saidenclosure portion and primary winding when said contacts are incircuit-making position, said current flow producing heat in saidenclosure portion for expansion of said fill and actuation of saidcontacts to circuit-interrupting position to produce interruption ofsaid current flow, said current interruption terminating said heatingaction for contraction of said fill and return of said contacts tocircuit-making position and the beginning or" another cycle, the pulsingflow of said thermoelectric current through said primary windingproduced by continuous cycling of said contacts being effective toinduce an alter nating current of higher voltage in said secondarywindmg.

5. Control apparatus, comprising in combination, a thermoelectricgenerator, a step-up tansformer having primary and secondary windings,relatively movable low resistance solid metal contacts havingcircuit-making and circuit-interrupting positions, temperatureresponsive contact actuating means for continuously cycling saidcontacts between said circuit-making and circuit-interrupting positions,said means comprising an electrically conductive heating member ofpredetermined electrical resistance, means connecting said contacts andheating member in circuit with said generator and the primary winding ofsaid transformer to effect current flow from said source through saidmember and primary winding when said contacts are in circuit-makingposition, said current flow producing heat in said member for actuationof said contacts to circuit-interrupting position and interruption ofsaid current flow, said current interruption terminating said heatingaction for return of said contacts to circuitmaking position and thebeginning of another cycle, the pulsing flow of said thermoelectriccurrent through said primary winding produced by continuous cycling ofsaid contacts being eifective to induce an alternating current of highervoltage in said secondary winding, a control circuit energized by saidalternating current, and a circuitcontrolling device in said controlcircuit, the higher voltage of said secondary Winding permittinglocation of said'cir'cuit controlling device remote from saidtransformer and control device.

6. Control apparatus for fluid fuel burning apparatus having main andpilot burners, comprising in combination, a thermoelectric generatorhaving at least one hot junction subject to the heat of burning fuel atsaid pilot burner, a transformer having primary and secondary windings,an electroresponsive fuel flow control device connected in circuit withsaid secondary Winding for control of the flow of fuel to said mainburner, relatively movable contacts having circuit-making andcircuit-interrupting positions, temperature responsive contact actuatingmeans for continuously cycling said contacts between said circuit-makingand circuit-interrupting positions, said means comprising anelectrically conductive heating member of predetermined electricalresistance, means connecting said contacts and heating member in circuitwith said source and the primary winding of said transformer to eifectthermoelectric current flow through said member and primary winding whensaid contacts are in circuit-making position, said current flowproducing heat in said member for actuation of said contacts tocircuit-interrupting position and interruption of said current flow,said current interruption terminating said heating action for return ofsaid contacts to circuit-making position and the beginning of anothercycle, the pulsing flow of said thermoelectric current through saidprimary winding produced by continuous cycling of said contacts beingeifective to induce an alternating current in said secondary winding forenergization of said electro-responsive control device.

7. Control apparatus for fluid fuel burning apparatus having main andpilot burners, comprising in combination, a thermoelectric generatorhaving at least one hot junction subject to the heat of burning fuel atsaid pilot burner, a transformer having primary and secondary windings,an electro-responsive fuel flow control device connected in circuit withsaid secondary winding for control of the flow of fuel to said mainburner, relatively movable contacts having circuit-making andcircuit-interrupting positions, temperature responsive contact actuatingmeans for continuously cycling said contacts between said circuit-makingand circuit-interrupting positions, said means comprising anelectrically conductive heating member of predetermined electricalresistance, means connecting said contacts and heating member in circuitwith said source and the primary winding of said transformer to effectthermoelectric current flow through said member and primary winding whensaid contacts are in circuit-making position, said current flowproducing heat in said member for actuation of said contacts tocircuit-interrupting position and interruption of said current flow,said current interruption terminating said heating action for return ofsaid contacts to circuit-making position and the beginning of anothercycle, the pulsing flow of said thermoelectric current through saidprimary winding produced by continuous cycling of said contacts beingeffective to induce an alternating current in said secondary winding forenergization of said electromesponsive control device, the circuitconnecting said secondary winding to said electroresponsive deviceincluding a full wave rectifier for changing said alternating current todirect current for delivery to said electroresponsive device.

8. Control apparatus for fluid fuel burning apparatus having main andpilot burners, comprising in combination, a thermoelectric generatorhaving at least one hot junction subject to the heat of burning fuel atsaid pilot burner, a step-up transformer having primary and secondarywindings, an electroresponsive fuel flow control device connected incircuit with said secondary winding for control of the flow of fuel tosaid main burner, a condition responsive circuit-controlling device incircuit with said flow control device for controlling energization ofthe latter, relatively movable contacts having circuit-making andcircuit-interrupting positions, temperature responsive contact actuatingmeans for continuously cycling said contacts between said circuit-makingand circuit-interrupting positions, said means comprising anelectrically conductive heating member of predetermined electricalresistance, means connecting said contacts and heating member in circuitwith said source and the primary Winding of said transformer to eflectthermoelectric current flow through said member and primary winding whensaid contacts are in circuit-making position, said current flowproducing heat in said member for actuation of said contacts tocircuit-interrupting position and interruption of said current flow,said current interruption terminating said heating action for return ofsaid contacts to circuit-making position and the beginning of anothercycle, the pulsing flow of said thermoelectric current through saidprimary winding produced by continuous cycling of said contacts beingefiective to induce a higher voltage alternating current in saidsecondary winding for energization of said electroresponsive controldevice, said higher voltage permitting location of said circuitcontrolling device remote from said transformer and flow control device.

9. In combination, a direct current source, a transformer having primaryand secondary windings, relatively movable solid metal contacts havingcircuit-making and circuit-interrupting positions, an hermeticallysealed expansible and contractible enclosure for said contacts having anelectrically conductive portion of predetermined electrical resistance,a temperature responsive expansible and contractible fluid fill for saidenclosure substantially non-conductive electrically and responsive tovariations in temperature for moving said contacts between saidcircuit-making and circuit-interrupting positions, and means connectingsaid contacts and enclosure.

portion in circuitwith said source and the primary winding, of, saidtransformer to effect current flow from said source through saidenclosure portion and primary winding when said contacts are incircuit-making position, said current flow producing heat in saidenclosure portion for actuation of said contacts to circuit-interruptingposition and interruption of said current flow, said currentinterruption terminating said heating action for return of said contactsto circuit-making position and the beginning of another cycle, thepulsing. current flow through said primary winding produced bycontinuous cycling of said contacts being effective to induce analternating current in said secondary winding.

10. In combination, a thermoelectric generator having at least onesemi-metallic element, a step-up transformer having. primary andsecondary windings, relatively movable solid metal contacts havingcircuit-making and circuit-interrupting positions, an hermeticallysealed expansible and contractible enclosure for said contacts having anelectrically conductive portion of predetermined electrical resistance,a temperature responsive expansible and contractible fluid fill for saidenclosure substantially nonconductive electrically and responsive tovariations in temperaturev for moving said contacts between saidcircuit-making and circuit-interrupting positions, and means connectingsaid contacts and enclosure portion in circuit with said generator andthe primary winding of said transformer to effect current flow from saidsource through said enclosure portion and primary winding when saidcontacts are in circuit-making position, said current flow producingheat in said enclosure portion for actuation of said contacts tocircuit-interrupting position and interruption of said current flow,said current interruption terminating said heating action for return ofsaid contacts to circuit-making position and the beginning of anothercycle, the pulsing flow of thermoelectric current through said primarywinding produced by continuous cycling of said contacts being effectiveto induce an alternating current of higher voltage in said secondarywinding.

11. In combination, a direct current source, a transformer havingprimary and secondary windings, relatively movable contacts havingcircuit-making and circuit-interrupting positions, an hermeticallysealed expansible and contractible enclosure for said contacts having anelectricaily conductive portion of predetermined electrical resistance,a temperature responsive expansible and contractible fluid fill for saidenclosure responsive to variations in temperature for moving saidcontacts between said circuit-making and circuit-interrupting positions,and means connecting said contacts and enclosure portion in circuit withsaid source and the primary winding of said transformer to eiiectcurrent fiow from said source through said enclosure portion and primaryWinding when said contacts are in circuit-making position, said currentflow producing heat in said enclosure portion for actuation of saidcontacts to circuit-interrupting position and interruption of saidcurrent flow, said current interruption terminating said heating actionfor return of said contacts to circuit-making position and the beginningof another cycle, the pulsing current flow through said primary windingproduced by continuous cycling of said contacts being efiiective toinduce an alternating current in said secondary Winding, and ambienttemperature responsive means opposing the response of said fluid fill tochanges in ambient temperature, thereby rendering cycling of saidcontacts independent of changes in the ambient temperature.

References Cited in the file of this patent UNITED STATES PATENTS.

952,778 Wohl et al Mar. 22, 1910 1,363,267 Porter Dec. 28, 19201,612,246 Whittingharn Dec. 28, 1926 2,273,996 Ross Feb. 24, 19422,366,881 Telkes Jan. 9, 1 945 2,375,569 McCarty May 8, 1945 2,440,265Gross Apr. 27, 1948 2,652,503 Pack Sept. 15, 1953 2,707,737 Rich et a1.May 3, 1955 2,717,123 Hilgert et a1 Sept. 6, 1955

